The present invention generally relates to an implantable cardiac lead for use with an implantable cardiac stimulation device. The present invention more particularly relates to such a lead adapted for use in the coronary sinus region of a heart and which employs a defibrillation electrode having a split configuration.
Implantable cardiac stimulation devices are well known in the art. Such devices may include, for example, implantable cardiac pacemakers and defibrillators. The devices are generally implanted in a pectoral region of the chest beneath the skin of a patient within what is known as a subcutaneous pocket. The implantable devices generally function in association with one or more electrode carrying leads which are implanted within the heart. The electrodes are usually positioned within the right side of the heart, either within the right ventricle or right atrium, or both, for making electrical contact with their respective heart chamber. Conductors within the leads couple the electrodes to the device to enable the device to sense cardiac electrical activity and deliver the desired therapy.
Traditionally, therapy delivery had been limited to the venous, or right side of the heart. The reason for this is that implanted electrodes can cause blood clot formation in some patients. If a blood clot were released arterially from the left heart, as for example the left ventricle, it could pass directly to the brain potentially resulting in a paralyzing or fatal stroke. However, a blood clot released from the right heart, as from the right ventricle, would pass into the lungs where the filtering action of the lungs would prevent a fatal or debilitating embolism in the brain.
Recently, new lead structures and methods have been proposed and even practiced for delivering cardiac rhythm management therapy to the left heart. These lead structures and methods avoid direct electrode placement within the left atrium and left ventricle of the heart by lead implantation within the coronary sinus region of the heart. As used herein, the phrase xe2x80x9ccoronary sinus regionxe2x80x9d refers to the venous vasculature of the left ventricle, including any portion of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.
It has been demonstrated that electrodes placed in the coronary sinus region of the heart may be used for left atrial pacing, left ventricular pacing, and cardioversion and defibrillation. These advancements enable implantable cardiac stimulation devices to address the needs of a patient population with left ventricular dysfunction and/or congestive heart failure which would benefit from left heart side pacing, either alone or in conjunction with right heart side pacing (bi-chamber pacing), and/or defibrillation.
When the ventricles of the heart are in need of defibrillation electrical therapy, it is desirable to deliver the defibrillation shock across as much of the ventricular myocardium as possible. If the defibrillation electrode combination includes either the case electrode or a superior vena cava defibrillation electrode, as is often practiced for the right heart, the defibrillation electrode for the left heart should have its distal end as near to the apex of the left ventricle as possible. In this example, this would then optimally position the defibrillation electrical field between the most myocardial tissue from the right heart to the left heart.
To maximize the usefulness of cardiac leads for implant in the coronary sinus region, the leads have included a pacing electrode to support left heart pacing for congestive heart failure. Since defibrillation electrodes are elongated as compared to pacing electrodes, the left ventricular pacing electrode has been located at the distal tip end of the lead, placing the left ventricular pacing electrode near to the left ventricular apex. While this is not an optimum pacing electrode placement, it has been found to be a more effective placement than a left ventricular pacing electrode placement proximal to the defibrillation electrode which, owing to the substantial link of the defibrillation electrode, would otherwise place the pacing electrode far up from the heart apex. An optimum left ventricular electrode placement would be between these extremes. As a result, it has been required that the defibrillation electrode extend from a point spaced from and proximal to the pacing electrode at the distal tip end. Hence, coronary sinus lead electrode placement has been a compromise, placing both the defibrillation electrode and pacing electrode in less than optimal locations for defibrillation and pacing when the lead is implanted in the coronary sinus region.
Leads for implant in the coronary sinus region may also provide left atrial therapy either alone or in addition to left ventricular therapy. These leads also include a left atrial pacing electrode and a left atrial defibrillation electrode.
The invention provides a chronic implantable cardiac lead for use in the coronary sinus region of a heart. The lead includes an elongated lead body having a distal end and a proximal end, a plurality of terminals at the proximal end of the lead body, an electrode assembly including a plurality of electrodes at the distal end of the lead body, and a plurality of conductors connecting each electrode to a respective given one of the terminals. The electrode assembly includes a pacing electrode proximally spaced from the distal end and a defibrillation electrode distal to the pacing electrode.
The present invention further provides an implantable cardiac lead for use in the coronary sinus region of the heart which locates both a defibrillation electrode for delivering a more optimal defibrillation electrical field for defibrillation and at least one pacing electrode for more optimal pacing. For ventricular defibrillation therapy, the lead includes an elongated defibrillation electrode which is split into first and second portions. The second portion extends to the distal tip of the lead to locate the defibrillation electrode for optimum defibrillation effectiveness near the left ventricular apex. At least one pacing electrode is positioned between the defibrillation electrode portions, placing the pacing electrode(s) to achieve effective pacing therapy in the middle of the left ventricle. The first portion of the defibrillation electrode is proximal to the pacing electrode so that it is positioned to cover the left ventricular base. Hence, both ventricular defibrillation and pacing therapy are rendered more optimally effective by the lead of the present invention.
The defibrillation electrode may, in accordance with one aspect of the present invention, be a coil electrode wherein the electrode portions are spaced apart electrical coils. Alternatively, in accordance with a further aspect of the present invention, the defibrillation electrode may be a plurality of ring electrodes with each electrode portion including a group of ring electrodes. At least one pacing electrode is then provided between the ring electrode groups.
The same lead configuration may also be employed for atrial therapy. Such an atrial lead would not have the length of a ventricular lead but the electrode configuration may be the same as described above.
Further, the present invention may be practiced to provide both atrial and ventricle therapy. Here, two electrode assemblies are provided on the lead, one for atrial pacing and defibrillation and the other for ventricular pacing and defibrillation. Each electrode assembly may include a defibrillation electrode split into spaced apart portions with at least one pacing electrode disposed in between the defibrillation electrode portions. The most distal ventricular defibrillation electrode portion preferably extends to or nearly to the distal tip end of the lead.
The lead, whether providing single chamber or dual chamber therapy, also preferably includes a plurality of connection terminals at its proximal end and a plurality of conductors for connecting each electrode with a respective different terminal. This permits the electrodes to be coupled to an implantable cardiac stimulation device configured to generate the required therapy to be applied by the electrodes.
The present invention still further provides an implantable cardiac stimulation system for use in stimulating a heart from the coronary sinus region of the heart. The system includes an implantable device that provides cardiac defibrillating energy, a lead having a distal end and a proximal end and an electrode assembly at the distal end of the lead. The electrode assembly includes a pacing electrode and a defibrillation electrode distal to the pacing electrode. The pacing and defibrillation electrodes may be coupled together when the device provides the defibrillating energy.